build: move vesin[torch] to the torch extra (fix conda-forge)

[wanghan-iapcm]

Summary

vesin's torch bindings ship as a separate PyPI package (vesin-torch, pulled in by the vesin[torch] extra). conda-forge packages vesin but not vesin-torch, so listing vesin[torch] in the core dependencies (added in #5491) breaks the conda-forge build of the base deepmd-kit package.

This moves vesin[torch] out of the core dependencies and into the torch optional-dependency extra (backend/find_pytorch.get_pt_requirement), so only deepmd-kit[torch] (pip) pulls it. The neighbor-list runtime already guards usage via is_vesin_torch_available(), and nlist_backend="auto" falls back to the native builder when vesin is absent, so this is behavior-preserving for installs that don't ship the torch extra.

Changes

• pyproject.toml: drop vesin[torch] from core dependencies.
• backend/find_pytorch.py: add vesin[torch] to the torch extra.

Known limitations

• No automated test covers the build-backend's generated extras; the change is verified by inspection (the pip install deepmd-kit[torch] resolution and the conda-forge recipe build are not exercised in CI here).
• When torch is not requested, the torch extra is empty and vesin is not installed (intended).

Summary by CodeRabbit

• Chores
  • Adjusted dependency configuration for improved package management.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 145f7e48-d06d-473f-a425-dc2dec7b3d05

📥 Commits

Reviewing files that changed from the base of the PR and between 2e3117e and 629a66c.

📒 Files selected for processing (2)

• backend/find_pytorch.py
• pyproject.toml

💤 Files with no reviewable changes (1)

• pyproject.toml

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📝 Walkthrough

Walkthrough

The PR relocates the vesin[torch] dependency from static project declarations in pyproject.toml to conditional inclusion in get_pt_requirement() within the backend module, making the dependency available only when PyTorch is unavailable during backend initialization.

Changes

Conditional vesin[torch] dependency handling

Layer / File(s)	Summary
Relocate vesin[torch] to conditional requirement backend/find_pytorch.py, pyproject.toml	get_pt_requirement() now includes vesin[torch] in the returned PyTorch dependency list with supporting comments, while the entry is removed from static project.dependencies to avoid duplication.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely identifies the main change: moving vesin[torch] from core dependencies to the torch extra to resolve a conda-forge compatibility issue.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.41%. Comparing base (2e3117e) to head (629a66c).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5501      +/-   ##
==========================================
- Coverage   81.42%   81.41%   -0.01%     
==========================================
  Files         871      871              
  Lines       96951    96952       +1     
  Branches     4240     4241       +1     
==========================================
- Hits        78941    78938       -3     
- Misses      16707    16711       +4     
  Partials     1303     1303              

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